1. Field of the Invention
This invention relates to an active-matrix type of liquid-crystal display using a thin-layer transistor (referred to as "TFT"), in particular a color liquid-crystal panel equipped with a color filter.
2. Description of the Related Art
The following will describe an example of an conventional active-matrix type of liquid-crystal panel disclosed in JPA 6-301057, by reference to FIG. 4.
A liquid-crystal layer 18 is sandwiched between a TFT substrate 21 and a counter substrate 22. On the TFT substrate 21 are formed source electrodes 7 and drain electrodes 6 made of metal, semiconductor layers 23 made of an amorphous material or the like, gate insulating films 3 made of silicon oxide or silicon nitride, gate electrodes 2 made of metal which are also a part of scanning lines, signal lines 20 made of metal, each of which contacts with the source electrode 7 and is orthogonal to scanning lines, and interlayer insulating films 24 for ensuring insulation between a scanning line and a signal line 20. On these are formed color filter layers 8 consisting of red, green and blue-colored insulating films (9, 10 and 11, respectively), on which are formed pixel electrodes 13 of transparent, electrically-conductive films made of indium-tin oxide (referred to as "ITO") or the like, electrically connecting with the drain electrodes 6.
Meanwhile, on the whole surface of an insulating substrate 15 is formed a counter electrode 16 of a transparent, conductive film made of such as ITO.
The TFT substrate 21 and the counter substrate 22 are put together via the liquid crystal layer with a thickness of 3 to 10 .mu.m.
FIG. 4 shows a coplanar type of TFT, but a reverse-staggered type of TFT is also common.
For the above panel, when a TFT is coplanar, rays from a back light or the like directly impinge on the back channel of the semiconductor layer in a translucent type of liquid-crystal display because there is nothing which blocks the rays on the back-channel side of the semiconductor layer in the liquid-crystal panel. When a TFT is a reverse staggered type, there is a color filter on the back-channel side of the semiconductor layer, but any of the red, green and blue filters cannot adequately shield the semiconductor layer from an external light. Thus, there exists a problem that both coplanar and reverse-staggered types of TFT may fail to normally function due to induction of an off-leak current in the semiconductor layer, resulting in a defective display.
To solve the above problem, it is effective to place a light-shielding layer for blocking incident rays on a TFT. JP-A 4-253028 discloses a liquid-crystal display utilizing such an approach. The liquid crystal display, however, has a problem that since pixel electrodes are formed inside of signal and scanning lines, the area through which rays pass is reduced, that is, a so-called aperture ratio is reduced, resulting in a darker display.